Specular reflection is a mirror-like reflection of light from a surface, in which light from a single incoming direction is reflected into a single outgoing direction. In the diagram to the right, a light ray is coming from the point P, and meets at the mirror at point O. The ray reflects at the point O outwards in the same medium towards point Q. If a line is put through point O that is at 90˚ to the mirror, the angles made by the light ray (shown in the diagram as θi{\displaystyle \theta _{i}} and θr{\displaystyle \theta _{r}}) must be equal. Both angles have to be equal whenever reflection occurs. This is known as the "law of reflection".